Polymorphism and cocrystal salt formation of 2-((2,6-dichlorophenyl)amino)benzoic acid, harvest of a second form of 2-((2,6-dimethylphenyl)amino)benzoic acid, and isomorphism between the two systems

Isomorphism and isostructurality were observed between form I of 2-((2,6-dimethylphenyl)amino)benzoic acid and its analog 2-((2,6-dichlorophenyl)amino)benzoic acid, which suggests double Cl–CH3 exchange also leads to structural similarity.

Tailoring adsorption induced phase transitions in the pillared-layer type metal-organic framework DUT-8(Ni)

Tailoring the characteristics of gating transitions in the porous network, Ni₂(ndc)₂dabco (ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane), also termed DUT-8(Ni) (DUT = Dresden University of Technology), was achieved by systematically adjusting the critical synthesis parameters. The impact of the starting composition and solvent mixtures in the synthesis was found to critically affect the guest-response properties of the obtained materials. A comprehensive set of physical characterization methods, namely thermal analysis, ¹H NMR of digested crystals, solid state ¹³C NMR, PXRD, SEM, IR and Raman spectroscopy shows that the crystallite size is a crucial factor, determining the differing characteristics such as "gate pressure" and adsorption capacity in the guest-responsive switching behaviour of DUT-8. Crystallites smaller than 500 nm in size retain the open form after removal of the guest molecules resulting in typical "Type Ia" isotherm, whereas crystallites larger than 1 μm transform into the "closed pore" form and therefore can show a characteristic "gate opening" behaviour during gas adsorption. The particle size distribution of DUT-8(Ni) can be tailored by changing the synthesis conditions and consequently the slope of the isotherm at the "gating step" is affected. The in depth analysis of synthesis conditions and switching behaviour is an important step towards a better understanding of the fundamental principles responsible for guest responsive porosity switching in the solid state.

Supramolecular assemblies of 2-hydroxy-3-naphthoic acid and N-heterocycles via various strong hydrogen bonds and weak X⋯π (X = C–H, π) interactions

Hydrogen bonds and weak X⋯π (X = C–H, π) interactions in a series of multi-component molecules constructed from 2-hydroxy-3-naphthoic acid with N-heterocycles are discussed in context.

Crystal structures of 1,4-diazabicyclo[2.2.2]octan-1-ium 4-nitrobenzoate dihydrate and 1,4-diazabicyclo[2.2.2]octane-1,4-diium bis(4-nitrobenzoate): the influence of solvent upon the stoichiometry of the formed salt

The 1:1 co-crystallization of 1,4-diazabicyclo[2.2.2]octane (DABCO) with 4-nitrobenzoic acid in ethanol–water (3/1) gave the salt dihydrate C6H13N2+·C7H4NO4−·2H2O, (1), whereas from methanol, the salt C6H14N22+·2C7H4NO4−, (2), was isolated. In (1), the cation and anion are linked by a strong N—H...O hydrogen bond, and the carboxylate anion is close to planar [dihedral angle between terminal residues = 6.83 (9)°]. In (2), a three-ion aggregate is assembled by two N—H...O hydrogen bonds, and the carboxylate anions are again close to planar [dihedral angles between terminal residues = 1.7 (3) and 5.9 (3)°]. Through the intervention of solvent water molecules, which self-assemble into helical supramolecular chains along thebaxis, the three-dimensional architecture in (1) is stabilized by water–DABCO O—H...N and water–carboxylate O—H...O hydrogen bonds, with additional stability afforded by C—H...O interactions. The global crystal structure comprises alternating layers of water molecules and ion pairs stacked along thecaxis. In the crystal of (2), the three-ion aggregates are assembled into a three-dimensional architecture by a large number of methylene–carboxylate/nitro C—H...O interactions as well as π–π contacts between inversion-related benzene rings [inter-centroid distances = 3.5644 (16) and 3.6527 (16) Å]. The cations and anions assemble into alternating layers along thecaxis.

Energetic multi-component molecular solids of tetrafluoroterephthalic acid with some aza compounds by strong hydrogen bonds and weak intermolecular interactions of C–H⋯F and C–H⋯O

Tetrafluoroterephthalic acid forming nine new crystals with a series of N-containing heterocycles including salts/co-crystals/hydrates is discussed in context.